42 A MANUAL OF PHYSIOLOGY 



readily than the red portion of the clot, and yields far more 

 fibrin-ferment on treatment with alcohol. 



But when we have traced the fibrin-ferment to the nucleo- 

 proteid of the leucocytes, and the fibrinogen to the plasma, 

 and have seen that the interaction of the two causes, first a 

 splitting up of the fibrinogen, and then the formation of 

 fibrin from its thrombosin constituent, we have not yet got 

 to the bottom of coagulation. We have still to ask what it 

 is that happens to the inert nucleo-proteid in the first 

 moments after the blood has been shed and converts it into 

 active fibrin-ferment. The researches of late years have 

 shown that a third factor is involved : calcium is present in 

 some form or oilier wherever coagulation occurs. The following 

 facts illustrate the role of the calcium : A solution of 

 fibrinogen free from calcium will not coagulate on the 

 addition of calcium-free nucleo-proteid, but will coagulate 

 if a soluble calcium salt be also added. The addition of 

 a soluble oxalate to blood ('2 or "3 per cent, potassium 

 oxalate) prevents coagulation by precipitating the calcium 

 as insoluble calcium oxalate. From plasma prepared in this 

 way a nucleo-proteid may be separated which contains little 

 or no calcium and does not cause coagulation, but which on 

 treatment with a calcium salt acquires the properties of 

 fibrin-ferment. The same is true of the nucleo-proteid 

 which can be extracted from so many organs by Wool- 

 dridge's method. And the most probable explanation of the 

 intravascular coagulation caused by the injection of nucleo- 

 proteid is that in the presence of the calcium salts of the 

 plasma it produces fibrin-ferment, although it has not-as yet 

 been conclusively shown that the amount of fibrin-ferment 

 obtainable from the blood is increased after injection of 

 nucleo-proteid. In the curious hereditary disease known as 

 haemophilia, a deficiency of calcium seems occasionally to 

 be responsible for the diminished coagulability of the blood ; 

 and the internal administration of a solution of calcium 

 chloride has sometimes been thought to lessen the tendency 

 to haemorrhage, or its local application to cut short an 

 actual attack. Injection of commercial peptone into the 

 veins of a dog, though not of a rabbit, deprives the blood 



